What is the plus (+) sign in permission in Linux ?

So do you see a plus sign in the permission section in any of your directory.
No need to get confused, well it just means that the directory has extra acl permission. We use acl to give individual permission for users or groups on any directory.
For eg.
I have a directory deepak inside my root home directory

# ls -l | grep deepak
drwxrwxr-x 2 deepak deepak  4096 Sep 24 16:14 deepak

Now I want to give a different user test additional rwx full permission on this directory so what am I suppose to do?
One option is that I will have to add test user to group owner of deepak directory but I really don't want to do that then in those case setfacl plays its role

# setfacl -m u:test:rwx /root/deepak
# ls -l | grep deepak
drwxrwxr-x+ 2 root root  4096 Sep 24 16:14 deepak

# getfacl /root/deepak
# file: root/deepak/
# owner: root
# group: root
user::rwx
user:test:rwx
group::r-x
mask::rwx
other::r-x

So as you can see all the acl details using the above command. For more detailed help and examples on setfacl follow the below link